ABSTRACT The overall aim of this application is to assess the role of the maternal and offspring genotype on the long-term impact of prenatal docosahexaenoic acid (DHA) on child growth and development through age 5 y. In order to achieve this, we propose to use information from the follow-up of a trial of prenatal DHA supplementation on child growth and development. This double-blind clinical trial, in which 1,094 pregnant women (18-35 y) who sought prenatal care at the Instituto Mexicano del Seguro Social General Hospital and related clinics in Cuernavaca, Mexico were randomized to receive either 400 mg of DHA or a placebo daily from mid pregnancy through delivery, was conducted between 2004 and 2005. A large body of information has been collected since including offspring anthropometric measurements at 5 different time points from birth to 5 y, as well as measures of global cognitive development at up to 3 different time points for over 80% of the life births (n=802/973). To this date the trial has resulted in heterogeneous effects on birth-weight and infant growth and global cognitive development, and more recently, a significant improvement in offspring's attention at 5 y. Besides the large pool of information available on child growth and development, we have information on maternal FADS genotype, which plays a key role in fatty acid metabolism and availability for the offspring at early stages, for approximately 700 mothers. For this analysis, we propose to use all the available data and assay the banked offspring biospecimens to demonstrate the role of both maternal and child FADS genotype on long-term growth and development within the context of a DHA supplementation RCT. We will use longitudinal data analysis techniques to assess the role of maternal and offspring Single Nucleotide Polymorphisms and haplotypes in the FADS region, on determining growth and development at different stages from birth to 5y, and as modulators of a prenatal DHA supplementation intervention. This represents a unique opportunity to broaden our understanding of the role of genetics on the metabolism of long-chain polyunsaturated fatty acids and its long-term impact on child development. Results from this study will potentially contribute to improve the design and targeting of DHA supplementation interventions and strengthen their public health impact.